1/*	$NetBSD: ssh-keysign.c,v 1.24 2022/10/05 22:39:36 christos Exp $	*/
2/* $OpenBSD: ssh-keysign.c,v 1.71 2022/08/01 11:09:26 djm Exp $ */
3
4/*
5 * Copyright (c) 2002 Markus Friedl.  All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28#include "includes.h"
29__RCSID("$NetBSD: ssh-keysign.c,v 1.24 2022/10/05 22:39:36 christos Exp $");
30#include <sys/types.h>
31
32#ifdef WITH_OPENSSL
33#include <openssl/evp.h>
34#endif
35
36#include <fcntl.h>
37#include <paths.h>
38#include <pwd.h>
39#include <stdarg.h>
40#include <stdio.h>
41#include <stdlib.h>
42#include <string.h>
43#include <unistd.h>
44#include <errno.h>
45
46#include "xmalloc.h"
47#include "log.h"
48#include "sshkey.h"
49#include "ssh.h"
50#include "ssh2.h"
51#include "misc.h"
52#include "sshbuf.h"
53#include "authfile.h"
54#include "msg.h"
55#include "canohost.h"
56#include "pathnames.h"
57#include "readconf.h"
58#include "uidswap.h"
59#include "ssherr.h"
60
61extern char *__progname;
62
63static int
64valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp,
65    u_char *data, size_t datalen)
66{
67	struct sshbuf *b;
68	struct sshkey *key = NULL;
69	u_char type, *pkblob;
70	char *p;
71	size_t blen, len;
72	char *pkalg, *luser;
73	int r, pktype, fail;
74
75	if (ret != NULL)
76		*ret = NULL;
77	if (pkalgp != NULL)
78		*pkalgp = NULL;
79	fail = 0;
80
81	if ((b = sshbuf_from(data, datalen)) == NULL)
82		fatal_f("sshbuf_from failed");
83
84	/* session id */
85	if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
86		fatal_fr(r, "parse session ID");
87	if (len != 20 && /* SHA1 */
88	    len != 32 && /* SHA256 */
89	    len != 48 && /* SHA384 */
90	    len != 64)   /* SHA512 */
91		fail++;
92
93	if ((r = sshbuf_get_u8(b, &type)) != 0)
94		fatal_fr(r, "parse type");
95	if (type != SSH2_MSG_USERAUTH_REQUEST)
96		fail++;
97
98	/* server user */
99	if ((r = sshbuf_skip_string(b)) != 0)
100		fatal_fr(r, "parse user");
101
102	/* service */
103	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
104		fatal_fr(r, "parse service");
105	if (strcmp("ssh-connection", p) != 0)
106		fail++;
107	free(p);
108
109	/* method */
110	if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
111		fatal_fr(r, "parse method");
112	if (strcmp("hostbased", p) != 0)
113		fail++;
114	free(p);
115
116	/* pubkey */
117	if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
118	    (r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
119		fatal_fr(r, "parse pk");
120
121	pktype = sshkey_type_from_name(pkalg);
122	if (pktype == KEY_UNSPEC)
123		fail++;
124	else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
125		error_fr(r, "decode key");
126		fail++;
127	} else if (key->type != pktype)
128		fail++;
129
130	/* client host name, handle trailing dot */
131	if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
132		fatal_fr(r, "parse hostname");
133	debug2_f("check expect chost %s got %s", host, p);
134	if (strlen(host) != len - 1)
135		fail++;
136	else if (p[len - 1] != '.')
137		fail++;
138	else if (strncasecmp(host, p, len - 1) != 0)
139		fail++;
140	free(p);
141
142	/* local user */
143	if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
144		fatal_fr(r, "parse luser");
145
146	if (strcmp(pw->pw_name, luser) != 0)
147		fail++;
148	free(luser);
149
150	/* end of message */
151	if (sshbuf_len(b) != 0)
152		fail++;
153	sshbuf_free(b);
154
155	debug3_f("fail %d", fail);
156
157	if (!fail) {
158		if (ret != NULL) {
159			*ret = key;
160			key = NULL;
161		}
162		if (pkalgp != NULL) {
163			*pkalgp = pkalg;
164			pkalg = NULL;
165		}
166	}
167	sshkey_free(key);
168	free(pkalg);
169	free(pkblob);
170
171	return (fail ? -1 : 0);
172}
173
174int
175main(int argc, char **argv)
176{
177	struct sshbuf *b;
178	Options options;
179#define NUM_KEYTYPES 5
180	struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
181	struct passwd *pw;
182	int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
183	u_char *signature, *data, rver;
184	char *host, *fp, *pkalg;
185	size_t slen, dlen;
186
187#ifdef __OpenBSD__
188	if (pledge("stdio rpath getpw dns id", NULL) != 0)
189		fatal("%s: pledge: %s", __progname, strerror(errno));
190#endif
191
192	/* Ensure that stdin and stdout are connected */
193	if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
194		exit(1);
195	/* Leave /dev/null fd iff it is attached to stderr */
196	if (fd > 2)
197		close(fd);
198
199	i = 0;
200	/* XXX This really needs to read sshd_config for the paths */
201	key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
202	key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
203	key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
204	key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY);
205	key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
206
207	if ((pw = getpwuid(getuid())) == NULL)
208		fatal("getpwuid failed");
209	pw = pwcopy(pw);
210
211	permanently_set_uid(pw);
212
213#ifdef DEBUG_SSH_KEYSIGN
214	log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
215#endif
216
217	/* verify that ssh-keysign is enabled by the admin */
218	initialize_options(&options);
219	(void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "",
220	    &options, 0, NULL);
221	(void)fill_default_options(&options);
222	if (options.enable_ssh_keysign != 1)
223		fatal("ssh-keysign not enabled in %s",
224		    _PATH_HOST_CONFIG_FILE);
225
226#ifdef __OpenBSD__
227	if (pledge("stdio dns", NULL) != 0)
228		fatal("%s: pledge: %s", __progname, strerror(errno));
229#endif
230
231	for (i = found = 0; i < NUM_KEYTYPES; i++) {
232		if (key_fd[i] != -1)
233			found = 1;
234	}
235	if (found == 0)
236		fatal("could not open any host key");
237
238#ifdef WITH_OPENSSL
239	OpenSSL_add_all_algorithms();
240#endif
241
242	found = 0;
243	for (i = 0; i < NUM_KEYTYPES; i++) {
244		keys[i] = NULL;
245		if (key_fd[i] == -1)
246			continue;
247		r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
248		    NULL, &key, NULL);
249		close(key_fd[i]);
250		if (r != 0)
251			debug_r(r, "parse key %d", i);
252		else if (key != NULL) {
253			keys[i] = key;
254			found = 1;
255		}
256	}
257	if (!found)
258		fatal("no hostkey found");
259
260	if ((b = sshbuf_new()) == NULL)
261		fatal("%s: sshbuf_new failed", __progname);
262	if (ssh_msg_recv(STDIN_FILENO, b) < 0)
263		fatal("%s: ssh_msg_recv failed", __progname);
264	if ((r = sshbuf_get_u8(b, &rver)) != 0)
265		fatal_r(r, "%s: buffer error", __progname);
266	if (rver != version)
267		fatal("%s: bad version: received %d, expected %d",
268		    __progname, rver, version);
269	if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
270		fatal_r(r, "%s: buffer error", __progname);
271	if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
272		fatal("%s: bad fd = %d", __progname, fd);
273	if ((host = get_local_name(fd)) == NULL)
274		fatal("%s: cannot get local name for fd", __progname);
275
276	if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
277		fatal_r(r, "%s: buffer error", __progname);
278	if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0)
279		fatal("%s: not a valid request", __progname);
280	free(host);
281
282	found = 0;
283	for (i = 0; i < NUM_KEYTYPES; i++) {
284		if (keys[i] != NULL &&
285		    sshkey_equal_public(key, keys[i])) {
286			found = 1;
287			break;
288		}
289	}
290	if (!found) {
291		if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
292		    SSH_FP_DEFAULT)) == NULL)
293			fatal("%s: sshkey_fingerprint failed", __progname);
294		fatal("%s: no matching hostkey found for key %s %s", __progname,
295		    sshkey_type(key), fp ? fp : "");
296	}
297
298	if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
299	    pkalg, NULL, NULL, 0)) != 0)
300		fatal_r(r, "%s: sshkey_sign failed", __progname);
301	free(data);
302
303	/* send reply */
304	sshbuf_reset(b);
305	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
306		fatal_r(r, "%s: buffer error", __progname);
307	if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
308		fatal("%s: ssh_msg_send failed", __progname);
309
310	return (0);
311}
312